Photoinitiator-Free Two-Photon Polymerization of Biocompatible Materials for 3D Micro/Nanofabrication

Two-photon polymerization is expected to realize the fabrication of biological tissues for regenerative medicine and drug development because of its capability of 3D fabrication with submicrometer spatial resolution. However, photopolymerization initiators generally added to resins have low biocompatibility and water solubility, which pose a challenge for the biological application of micro- and nanostructures fabricated by photopolymerization. In this study, two-photon polymerization is performed using biocompatible materials without photoinitiators and the preservation of the material properties of the fabricated 3D structures is evaluated. Poly(ethylene glycol) diacrylate (PEGda) and collagen are successfully fabricated using a femtosecond pulsed laser at a wavelength of 400 nm with a feature size of 100 nm without photoinitiator. The excitation intensities required for the polymerization of PEGda and collagen are about 450 and 150 kW cm(-2), respectively, which are smaller than those reported with using photoinitiators. Raman spectroscopy is used to confirm that the water-swelling polymer network of PEGda and the enzymatic degradation of collagen, which are important factors in the application with live cells, are maintained in the fabricated structures.